<!doctype html>
<html>
<meta charset="utf-8">
<head>
<title>3DLUT Base Cube Maker</title>
<style>
canvas {
  min-width: 512px;
  min-height: 64px;
  image-rendering: pixelated;
}
#cube {
  max-width: calc(100% - 20px);
  overflow: auto;
}
</style>
</head>
<body>
<h1>Color Cube Image Maker</h1>
<div>size:<input id="size" type="number" value="8" min="2" max="64"/></div>
<p><button type="button">Save...</button></p>
<div id="cube"><canvas></canvas></div>
<div>( note: actual image size is
<span id="width"></span>x<span id="height"></span> )</div>
</p>
</body>
<script type="module">

const ctx = document.querySelector( 'canvas' ).getContext( '2d' );

function drawColorCubeImage( ctx, size ) {

	const canvas = ctx.canvas;
	canvas.width = size * size;
	canvas.height = size;

	for ( let zz = 0; zz < size; ++ zz ) {

		for ( let yy = 0; yy < size; ++ yy ) {

			for ( let xx = 0; xx < size; ++ xx ) {

				const r = Math.floor( xx / ( size - 1 ) * 255 );
				const g = Math.floor( yy / ( size - 1 ) * 255 );
				const b = Math.floor( zz / ( size - 1 ) * 255 );
				ctx.fillStyle = `rgb(${r},${g},${b})`;
				ctx.fillRect( zz * size + xx, yy, 1, 1 );

			}

		}

	}

	document.querySelector( '#width' ).textContent = canvas.width;
	document.querySelector( '#height' ).textContent = canvas.height;

}

drawColorCubeImage( ctx, 8 );

function handleSizeChange( event ) {

	const elem = event.target;
	elem.style.background = '';
	try {

		const size = parseInt( elem.value );
		if ( size >= 2 && size <= 64 ) {

			drawColorCubeImage( ctx, size );

		}

	} catch ( e ) {

		elem.style.background = 'red';

	}

}

const sizeElem = document.querySelector( '#size' );
sizeElem.addEventListener( 'change', handleSizeChange, true );

const saveData = ( function () {

	const a = document.createElement( 'a' );
	document.body.appendChild( a );
	a.style.display = 'none';
	return function saveData( blob, fileName ) {

		const url = window.URL.createObjectURL( blob );
		a.href = url;
		a.download = fileName;
		a.click();

	};

}() );

document.querySelector( 'button' ).addEventListener( 'click', () => {

	ctx.canvas.toBlob( ( blob ) => {

		saveData( blob, `identity-lut-s${ctx.canvas.height}.png` );

	} );

} );

</script>
</html>
